leetcode5

public class Solution {
        private int lo, maxLen;

        public String LongestPalindrome(String s)
        {
            int len = s.Length;
            if (len < )
                return s;

            for (int i = ; i < len - ; i++)
            {
                extendPalindrome(s, i, i);  //assume odd length, try to extend Palindrome as possible
                extendPalindrome(s, i, i + ); //assume even length.
            }
            return s.Substring(lo, maxLen);
        }

        private void extendPalindrome(String s, int j, int k)
        {
            while (j >=  && k < s.Length && s[j] == s[k])
            {
                j--;
                k++;
            }
            if (maxLen < k - j - )
            {
                lo = j + ;
                maxLen = k - j - ;
            }
        }
}

https://leetcode.com/problems/longest-palindromic-substring/#/description

补充一个python的实现，使用动态规划解决：

 class Solution:
     def longestPalindrome(self, s: 'str') -> 'str':
         n = len(s)
         dp = [[False for _ in range(n)]for _ in range(n)]
         count =
         res = ''
         for i in range(n):
             dp[i][i] = True
             if count < :
                 res = s[i]
                 count = 

         for i in range(n-):
             if s[i] == s[i+]:
                 dp[i][i+] = True
                 if count < :
                     res = s[i:i+]
                     count = 

         for k in range(,n+):
             for i in range(n-k+):
                 j = i + k -
                 if s[i] == s[j] and dp[i+][j-]:
                     dp[i][j] = True
                     if count < j +  - i:
                         count = j +  -i
                         res = s[i:j+]
         return res